A radiological characterization device comprising at least one collimated radiological measuring probe, a sensitive end of which is placed in an exchangeable collimator having an opening and a field of observation. The collimator is carried by a collimator holder, the assembly consisting of collimator and collimator holder being inserted in a stack between two shielding screens, the shielding screens being exchangeable so as to adjust the thickness thereof, the assembly consisting of collimator and collimator holder and the shielding screens providing protection for the probe vis-à-vis parasitic ionizing radiation coming from ionizing radiation sources situated outside the field of observation of the collimator.
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1. Radiological characterization device comprising at least one collimated radiological measuring probe, a sensitive end of which is placed in an exchangeable collimator with an observation field, characterized in that the collimator is carried by a collimator holder, the assembly consisting of collimator and collimator holder being inserted in a stack between two shielding screens, the shielding screens being exchangeable so as to adjust the thickness thereof, the assembly consisting of collimator and collimator holder and the shielding screens providing protection of the probe vis-à-vis parasitic ionizing radiation coming from ionizing radiation sources situated outside the field of observation of the collimator, the collimator being substantially in a u shape with an opening and a bottom at which the sensitive end of the measuring probe is housed.
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This application is a National Phase of PCT/EP2010/053104, filed Mar. 11, 2010, entitled, “DEVICE FOR X-RAY CHARACTERISATION PROTECTED AGAINST PARASITIC IONISING RADIATION SOURCES”, and which claims priority of French Patent Application No. 09 51594, filed Mar. 13, 2009, the contents of which are incorporated herein by reference in their entirety.
The present invention concerns a phased array ultrasonic contact transducer.
The present invention concerns a radiological characterisation device protected against parasitic ionising radiation sources. Radiological characterisation means that it will be possible with the device, to make quantitative measurements, that is to say of dose rate, and measurements on the quality of radioelements present by means of spectrometry.
Work in hostile environments is frequent in the nuclear industry, in particular in operations of dismantling nuclear installations. These operations are of course framed by rules, practices and optimisation methods, for example by the application of the ALARA (as low as reasonably achievable) principle. This principle was established by the industry in order to reduce exposure to ionising radiation so that it is as low as possible having regard to economic and social factors. In practice, the technical operations depend on mastery of the context and more precisely the in situ radiological characterisation, that is to say knowledge of the level of concentration of the contamination and the location thereof as well as the quality of the radioelements present in a given place.
There exist radiological characterisation devices such as the ones described in French patent application FR 2 879 304, which associate a gamma camera with a collimated gamma spectrometry detector, the collimator having an observation field that is included in the observation field of the gamma camera. In this device, the collimator is fixed and surrounds the gamma spectrometry detector. The document “Characterisation and modelling of a radioactive site by combined use of the EDR unidirectional gamma scanner and the VISIPLAN 3D planning tool”, F. Vermeersch et al, 2003, shows the use of a gamma analyser in which a gamma detector of the CsTi crystal type coupled with a photodiode is housed in a steel casing equipped on its front face with frustoconical shielding, this shielding being extended by a steel collimator. It is clear that, in order to reveal ionising radiation sources of very different levels, as can be found in buildings being dismantled, it is necessary to have available collimators of different interchangeable sizes.
A radiological characterisation device called Radscan 600 is also known, illustrated in FIG. 1 of the U.S. Pat. No. 7,095,030. The device has an inspection head that includes a video camera, a collimated gamma detector and a laser telemetry device. In this device the collimator is interchangeable. The drawback of this device is that, in operation, hot spots of lower intensity may be masked by more intense hot spots outside the field of observation of the collimator.
The aim of the present invention is to propose a radiological characterisation device that does not have the above limitations and difficulties, and in particular that is capable of characterising ionising radiation sources even of lower intensity in the presence of more intense ionising radiation sources without being interfered with by parasitic noise.
Another aim of the invention is to propose a radiological characterisation device with an adjustable collimator.
Another aim of the invention is to propose a radiological characterisation device with an interchangeable radiological measuring probe.
To achieve this, the present invention is a radiological characterisation device comprising at least one collimated radiological measuring probe, a sensitive end of which is placed in an interchangeable collimator having an observation field and an opening. The collimator is carried by a collimator holder and the assembly consisting of collimator and collimator holder is inserted in a stack between two shielding screens, the screens providing the shielding being exchangeable so as to adjust the thickness thereof, the assembly consisting of collimator and collimator holder and the shielding screens providing protection for the probe vis-à-vis parasitic ionising radiation coming from ionising radiation sources situated outside the observation field of the collimator.
Collimators having openings for different sizes may be housed in the collimator holder.
Advantageously, the measuring probe is also exchangeable.
The measuring probe may be a gamma spectrometry probe or a dose rate probe.
The radiological characterisation device preferably also comprises a removable probe holder in which the probe is placed, the probe holder, when it is housed in the collimator, making it possible to position the sensitive end of the probe in the collimator.
When the probe holder houses several probes, they are arranged in a bundle.
Advantageously, each shielding screen comprises one or more shielding plates; when there are several plates, they are in a stack. It is thus possible to adjust the thickness of the shielding screen.
The collimator can be substantially in a U shape with an opening and a base.
A shielding plate adjacent to the collimator may be bevelled in the vicinity of the collimator opening in order to increase the observation field thereof.
One of the shielding screens comprises a through hole in which the probe passes.
It is possible to provide means of locking the shielding screens in terms of rotation and translation with respect to the collimator holder and collimator.
The radiological characterisation device may also comprise a visible or infrared camera and/or a telemetry device secured to the locking means and/or a spotlight. They are very useful during the examination of complex scenes.
It is preferable also to provide means of locking the probe when it is in place in the collimator, so as to be able to move the characterisation device without any problems.
The present invention will be better understood from a reading of the description of example embodiments given, for purely indicative and in no way limitative purposes, with reference to the accompanying drawings, in which:
The various configurations shown of the radiological characterisation device must be understood as not being exclusive of one another.
Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate passing from one figure to another.
The various parts shown in the figures are not necessarily shown according to a uniform scale, in order to make the figures more legible.
Reference will be made to
The opening 2.1 of the collimator 2 is situated at one edge of the stack 4. The radiological characterisation device also comprises at least one radiological measuring probe 6 having a sensitive part housed in the collimator 2 at the bottom of the U, the opening 2.1 of the collimator 2 being free. This measuring probe 6 is also exchangeable. This measuring probe 6 may be a dose rate measuring probe, for example the probe SHI from the company Saphymo. In a variant, it may be a gamma spectrometry probe based on semiconductors such as for example CdZnTe. It is possible to use simultaneously several gamma spectrometry probes 6 arranged in a bundle 7 as will be seen subsequently. A probe holder 8 is preferably provided for positioning, with precision, the probe 6 (or the probes) in the collimator 2, which offers the possibility of using measuring probes 6 that do not have the same transverse sections. The probe holder 8 is removable and may take the form of a sleeve in which the measuring probe 6 or the bundle 7 of measuring probes is inserted, the assembly consisting of probe holder 8 and measuring probe 6 being housed in the collimator 2 at the bottom of the U. This probe holder 8 can be produced from a material such as copper, which makes it possible also to filter ionising radiations with the lowest energies.
The probe holder 8 can be associated with a given measuring probe 6; it has an outside transverse section that corresponds to the space delimited by the bottom of the collimator 2 and an inside transverse section that corresponds to the transverse section of the measuring probe 6 or of the bundle 7 of measuring probes. The assembly consisting of probe holder 8 and measuring probe 6 will hereinafter be referred to as the measuring assembly 11. The measuring assembly 11 bears on the shielding screen 5 fitting on top of the collimation assembly 3.
The two shielding screens 5 and the collimation assembly 3 protect the measuring probe 6 from any parasitic ionising radiation coming from ionising radiation sources placed outside the field of observation of the collimator 2. The two shielding screens 5 can each be formed by one or more plates 5.1; when there are several plates 5.1, they are in a stack. The shielding screens 5 and the collimator holder 1 will be produced from a material forming an obstacle to ionising radiation, such as lead for example. The collimator 2 can be made from tungsten for example.
One of the shielding screens 5 comprises a through hole 5.2 through which the measuring probe 6 passes, together with the probe holder 8 if such exists.
The number of shielding plates 5.1 is not necessarily the same on either side of the collimation assembly 3.
It is possible to provide that at least one shielding plate 5.1, the closest possible to the collimator 2, has a bevelled edge 5.3 at the opening 2.1 of the collimator 2 so as to increase the observation field of the collimator 2.
Locking means 9 can also be provided for locking the various constituents of the stack 4 with respect to both rotation and translation. The locking means 9 comprise a lower plate 9.1 from which three centring rods 9.2 project. They pass through the shielding screens 5 and the collimator holder 1. These centring rods 9.2 prevent rotation of one of the constituents of the stack 4 with respect to the others. The stack 4 rests on the lower plate 9.1. In the example three centring rods 9.2 have been shown.
These locking means 9 also comprise an upper plate 9.3 through which the centring rods 9.2 pass. It is intended to fit on top of the stack 4. Nuts 9.4 are also found, to be screwed onto the centring rods 9.2, which are threaded at least locally in order to hold the upper plate 9.3 pressed against the shielding screen 5 that it covers. Means 10 of locking the measuring probe 6 are also provided, which can take the form of a bar 10.1 one end of which is provided with a through hole 10.2 for fitting it onto one of the centring rods 9.2 and the other end of which is provided with a recess 10.3 intended to be fixed on the other centring rod 9.2. The bar 10.1, when it is in the locking position, is held pressed on the upper plate 9.3 by means of the nuts 9.4 that are screwed on the centring rods 9.2. It prevents the measuring probe 6 moving in translation.
The upper plate 9.3 can be provided with a handle 9.30 for facilitating movement of the characterisation device and the angular orientation of the collimator 2 and more particularly of the opening 2.1 thereof.
The stack 4 has been shown in the form of a cylinder of revolution but this is not limitative. The shielding screens 5 can in this case take the form of discs.
With such a device, it is easy to modify the number of shielding plates 5.1 according to the configuration of the space in which the radiological characterisation device that is the subject matter of the invention is used. It is thus possible to add shielding plates 5.1 between the lower plate 9.1 and the collimation assembly 3, if a very intense ionising radiation source (not shown) is situated under the device. It will of course be possible to add them between the upper plate 9.3 and the collimation assembly 3, if the very intense ionising radiation source is situated above the device. Thus the two shielding screens 5 do not necessarily have the same thickness, as illustrated in
In
The efficacy of a collimation assembly 3 with a collimator 2 having an opening, that is to say an aperture, of 90° has been verified by means of a series of calculations using the MERCURE advanced computing code 6.2. This is a computing code for evaluating, for an ionising radiation source having a given energy, the gamma fluence rate at the detector. It will be recalled that fluence is, at a given point in space, the quotient of the number of particles that, in a given interval of time, enter a suitably small sphere centred at this point, divided by the area of the great circle of this sphere. The fluence rate is the quotient of the variation in the fluence divided by the unit of time.
The ionising radiation source has a large volume, 10 metres by 6 metres by 2 metres. The dose rate measuring probe is placed at 1 metre from the ionising radiation source. The ionising radiation source has been given five discrete energy values, namely 100 keV, 500 keV, 1 MeV, 2 MeV and 10 MeV. These fluence rate calculations have been made with the radiological characterisation device of the invention, the collimator being in place or absent. The graph in
Still using the same ionising radiation source and the radiological characterisation device that is the subject matter of the invention, it was attempted to evaluate the signal to noise ratio afforded by the collimation assembly. Reference is made to
It will now be shown, with reference to
In
The measuring probe 6 receives the gamma spectrum emitted by the ionising radiation source (not shown). The signals supplied by the measuring probe in response to the gamma spectrum received make it possible to estimate the flux rate or the activity of each radioelement emitting ionising radiation present in the spectrum. Thus the interpretation of the gamma spectrum makes it possible, for example during a phase of cleaning a room, to monitor “in line” each radioelement present in the spectrum received.
The radiological characterisation device that is the subject matter of the invention can be used by directly exploiting the signals delivered by the measuring probe or probes and providing the processing of these signals “in line” by means of a simple report or table. An absolute measurement method is used. The radiological characterisation device is moved over at least one vertical in front of the scene to be characterised, hanging it from a pole and giving it one or more angular orientations per height. According to the signals delivered, it is possible to change the collimator, the thickness of one or other or both shielding screens or even the measuring probe.
In a variant, it is possible to carry out a posteriori processing. A relative measurement method is used. For a given ionising radiation source and a given collimator, a mapping of the scene observed will be drawn up in terms of dose rates. A definition will be made of the orientation angles that will be given to the characterisation device and therefore to the measuring probe, on either side of a zero angle in which the axis of sight of the collimator is substantially normal to the scene observed. A plurality of heights are also defined. For example, a measurement is made of the dose rate for a given height and a certain number of orientation angles. It is thus possible to trace a first mapping as illustrated in
In
In
The cleaning operations have continued, the vessel has been rinsed and the efficacy of the rinsing cannot be denied in
It will be understood that various changes and modifications can be made to the radiological characterisation device without departing from the scope of the invention.
Brenneis, Christophe, Ducros, Christian, Lamadie, Fabrice, Girones, Philippe
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